1. Field of the Invention
The present invention relates to a method for producing a fuse element made of different kinds of metal and used specifically in the principal part of a fuse and to a fuse element produced with the method.
2. Description of the Related Art
A method for producing a fuse element made of different kinds of metal is disclosed in, for example, Japanese Patent Unexamined Patent Publication No. Hei. 3-102729. As shown in FIG. 4(A), a tape-like through-lay type composite material 5 is used in the method in Hei. 3-102729. The tape-like through-lay type composite material 5 comprises a fuse alloy 1 arranged in the center of the material 5 and copper 3 arranged on both sides of the fuse alloy 1 as a lead piece. Window holes 7 are bored at predetermined intervals in the longitudinal direction of the tape-like through-lay type composite material 5 so that the fuse alloy 1 can have a predetermined volume, then a material 9 is obtained as shown in FIG. 4(B). Next, as shown in FIG. 4(C), a part of the fuse alloy 1 in the material 9 is sealed up with epoxy resin 11. Finally, as shown in FIG. 4(D), the material 9 is cut with a press accordingly at an even interval in the longitudinal direction, then a fuse 13 is obtained.
Nevertheless, the method of producing the aforementioned fuse element makes it essential to use the tape-like through-lay type composite material as a stock. In order to obtain the tape-like through-lay type composite material, copper as a lead piece is welded by electron-beam onto both the lateral sides of the fuse alloy disposed in the center of the fuse element. The electron-beam welding generally requires a vacuum chamber because a heat source is energy derived from the high-speed electron beams generated in a vacuum. Therefore, as well as production facilities for them, such fuse elements costs much. On the other hand, non-vacuum electron-beam welding-machines is developed and makes welding operation possible under the atmospheric pressure. However, the non-vacuum electron-beam welding machines requires attention to protect against X-rays.
In addition, electron-beam welding tends to cause porosity in products because the rate of solidification in the weld is high, which results in making bubbles hardly escapable from the fusion-welded portion. Another problem still arises from the formation of unevenness within the boundary between the different kinds of metal if a density of the beam energy is unstable. Therefore, these undesirable factors have made it difficult to obtain high-precision fuse elements.
In view of the aforementioned situation, an object of the present invention is to provide a method for producing an inexpensive precision fuse element made of different kinds of metal. In addition, a further object is to provide a fuse element produced with the same.
The above object of the present invention can be attained by a method for producing a fuse element having a fusible portion and any other portion which are made of different kinds of metal. The method comprises the steps of boring a through-hole in a substrate made of a first metal, forming an element plate by fusion-bonding a second metal to the through-hole and integrally stamping a pair of substrate portion made of the first metal and a low-melting-point portion made of the second metal. The second metal is made of a metal whose melting point is lower than that of the first metal. Further, the pair of substrate portion is connected together by the low-melting-point portion so that the fuse element is formed.
Through this method, a fuse element made of different kinds of metal can be formed without using a tape-like through-lay type composite material which necessitates using electron-beam welding. Moreover, since the low-melting-point metal is fusion-bonded to the through-hole thus bored by stamping, it is possible to form a boundary free from unevenness between the different kinds of metal which tends to develop at the time welding.
In the above method, it is preferable that the step of forming the element plate comprises the steps of providing a low-melting-point metal chip substantially the same shape as the through-hole, inserting the low-melting-point metal chip into the through-hole and fusion-bonding the low-melting-point metal chip to the through-hole by heat-melting the low-melting-point metal chip.
Through this method, the low-melting-point metal chip substantially similar in configuration to the through-hole is formed beforehand and heat melted so as to fusion-bonded to the through-hole, whereby the fusible portion is formed of low-melting-point metal having a constant volume at all times.
Furthermore, in the above step of forming the element plate, it is also preferable that the low-melting-point metal chip is provided by stamping a uniform-thickness plate made of the second metal.
In above step of forming the element plate, it is also preferable that injecting and fusion-bonding a melted second metal into the through-hole.
Furthermore, in the above method for producing a fuse element, it is more preferable that the low-melting-point metal portion is stamped out so as to have a small-width portion whose width is narrower than one of a large-width portion which is defined at a edge portion of the low-melting-point metal portion adjacent to the substrate portion.
In the above method for producing a fuse element, it is more preferable that the small-width portion is formed in the substatially center portion of the low-melting-point metal portion.
The above further object of providing a fuse element is can be attained by a fuse element produced by a method comprising the steps of boring through-hole in a substrate made of first metal, forming an element plate by fusion-bonding a second metal to the through-hole, the second metal made of a metal whose melting point is lower than that of the first metal, and integrally stamping a pair of substrate portion made of the first metal and a low-melting-point portion made of the second metal. The pair of substrate portion is connected together by the low-melting-point portion so that the fuse element is formed. The fuse element has a small sectional area portion whose sectional area is smaller than that of any one of both end portions of the low-melting-point metal portion.
With this fuse element, the small sectional area portion is formed in the fusible portion and certainly fused and broken, so that visual inspection can be improved at the time of fusing.
Furthermore, it is more preferable that the small sectional area portion is formed in a substantial center portion of said low-melting-point-metal portion.
It is also preferable that the substrate is in a form of a flat plate.
Furthermore, it is more preferable that the substrate is in a form of a plate having a recessed cross section in a thickness direction of said substrate.
It is also preferable that the recessed cross section is U-shaped in a cross section.